Abstract: The Pentagon was constructed between September 1941 and January 1943. A substantial renovation of the entire 6.6 million sq ft (610,000 sq m) facility began in 1999 and was scheduled for completion in 2010. On September 11, 2001, a hijacked commercial airliner crashed into the building. One-hundred eighty-nine persons were killed and a portion of the building was damaged by the associated impact, deflagration, and fire.